Fixing Painted Metal Parts

Many of the painted parts were gouged, bent or just plain broken. Parts showing the most damage were the footpegs and the center stand, which should be no surprise. I heated these items with a torch and put them back to their original shape. The seat pan threaded inserts had been broken out and UNC bolts were brazed on to the pan. I removed the bolts, sandblasted and cleaned the metal, and then TIG welded the cracks in the pan together. This was difficult since braze was in the metal which caused popping and pitting of the welds.  When the pan was as good as I could get it, I welded plates with threaded inserts onto the pan. 

The seat pan rebuilt, refit, and ready to paint. 

The oil tank was also in pretty rough shape. When the previous owner put an oversized knobby on the rear it rubbed against the welded seam around the tank. Eventually it wore a hole through the tank. I found the tank leak when I cleaned it with kerosene and fluid leaked onto my bench. To clean the inside of the tank I filled it with engine degreaser and then power washed it. To dry the metal before it had time to rust I put the tank in my gas grill. I only lit one burner and put the tank on the side without the flame. When it reached 300 degrees I shut it off and let it cool. This completely dried out the inside of the tank. I then TIG welded the seam and the mounting bracket, which was also broken. After it cooled I put Marvel Mystery Oil in the tank to check the seal and prevent rust. This process was all completed within 24 hours so the tank did not have time to rust.

The weld seam worn through from the oversize knobby. 

Tig welded, sealed and ready to paint. 

Rebuilding the Swingarm

A fixture for the swingarm was made for measurement on a surface plate to factory specs. It was bent up about 5/16 of an inch on the chain side.  It was hard to see how this had happened as the tubes were square with the surface plate up to the axle section that is brazed on to them. I heated it cherry red and bent it back to the proper location. This movement closed up the axle slot which had to be worked back out to size on a mill. When all was finished it was within a 1/16 of parallel which I thought was good. The axle slots had also been gouged out significantly. This was partially done when I tried to remove the dummy axle which was severely rusted in place. I heated it up but still pulled all the threads trying to get it out. Previously I had tried nut and bolt breaker with no effect. I TIG welded the gouges and milled everything back to its original state.

Inspecting the swingarm to factory specs. 

I had never replaced the silent bloc swingarm bushings on a BSA and thought I would give it a try as mine were quite a ways off center. I thought I might as well learn everything possible on this bike. Silent blocs are a pretty odd setup. There is not a bushing that pivots in the swingarm, but rubber molded between two pieces of steel that flex and allow radial movement. This turned out to be pretty tough, at least the way I attempted it. I tried the method demonstrated in the workshop manual. Grab and twist. No results at all. I made a mandrel on a lathe slightly smaller than the diameter of the bushing and attempted to press it out. This worked for the center tube only. Bummer. This left the outer steel in the swingarm, which I broke loose with a screwdriver, chisel and heating it with a torch. I’m sure it looked like 3 stooges bike repair attempting the job, but I have the comfort of knowing no one was watching. I even debated discussing it here to be honest but hope I stop someone else from making the mess of their swingarm that I did. I was eventually able to get the bushings out, but I tore up the swingarm. This had to be fixed with an air grinder on the inside and my old friend the TIG welder on the outside. I’m glad I learned how to weld in college. The next time I do this I will rethink my strategy and I do not have a plan at the present time. 

 Bushings removed, the swingarm welded and ground back to its original form. 

Chain side bent back to position, welded and milled to specs. 

Outside of the swingarm welded and benched back to its original form. 

Inspecting and Fixing the Frame

The first thing I noticed with the frame was that it had no side stand or lug. It still had a center stand but it was bent. I bought a replacement lug on eBay and then modified its contour to match the one on my 1970 Lightning. It’s nice to have a bike for comparison when parts are mangled or missing. Although the Hornet had most of its pieces, it had been reworked and I was not sure what was original and what was not.

I purchased a side stand off of eBay and then tac welded the lug onto the frame in a position that matched the Lightning's orientation. This was done before my “rough assembly”.  After the frame was broken down to its components I TIG welded it permanently into place.

New lug tack welded into position. 

Reconfigured on a mill to match the original lug. 

Fully welded into place and blended to the frame with air grinders. 

I made several BSA frame tools based on prints in my BSA workshop manual. The backbone gauge highlighted a slight bend in the frame. It was not enough to be an issue or require repair. Frame bushings were machined to mount the frame on a surface plate for inspecting dimensions to the factory prints. Overall everything looked good, and aside from adding the side stand lug and fixing bent brackets, it was ready to go. 

Checking the steering head angle on a granite surface plate. 

Inspecting side to side dimensions with a height gauge.